Hot cathode tube with metal envelope



June 21, 1938. E. F. LowRY HOT CATHODE TUBE WITH METAL ENVELOPE Filed Jan. 4, 193e lNvENToR frN/n F 0N/1y.

A'TTONE WITNESSES:

wa/ ,JM @J4 @ma Cil Patented .lime 21. 1938 UNITED STATES HOT CATHODE TUBE WITH METAL ENVELOPE Erwin F. Lowry, Forest Hills, Pa., assigner to Westinghouse Electric & Manufacturing Cornpany, East Pittsburgh, Pa., a corporation of Pennsylvania Application January 4, 1936, Serial No. 57,537

9 Claims.

This invention relates to gas-filled discharge tubes and particularly to such tubes having a metallic envelope.

It is an object of this invention to provide an arrangement of the tube electrodes in which the two principal electrodes are electrically separated rom one another by the seal which joins the two main parts of the envelope.

It is a further object of this invention to s0 arrange the electrode that spacings may be closer and the structure more rigid than heretofore.

It is a further object of this invention to make use of a directly heated cathode structure, having an electrostatic guard to produce delayed action, and to support such structure by a metal plate through which the cathode is electrically united with a portion of the envelope.

It is a further object of this invention to utilize a cathode structure which extends substantially across the whole diameter of the tube and electrically to unite such structure with the envelope.

It is a further object of this invention to provide a seal made of several parts of different insulating material and to prolong the innermost part into a skirt within the tube, thereby aiording a long creepage path within the tube between the two main electrodes.

It is a further object of this invention to provide a seal including several insulating materials, at least one of which makes a sealing union with the metal of the envelope.

It is a further object of this invention to provide a duct for pumping the tube which also serves as a conductor to one of the electrodes.

Other objects of the invention and details of thc structure will be apparent from the following description and the drawing in which:

Figure 1 is a vertical section through one form of my device;

Fig. 2 is a similar section through a modification; and

Fig. 3 is a similar section showing another application of the device.

In Fig. l, a part i of the envelope constitutes the anode and the cathode is electrically united to another part 2 of the envelope. Between the parts I and 2 are two rings 3 and 4, the ring 3 being welded to the part I and the ring 4 to the part 2. Each ring comprises a portion contacting the edge of the adjacent part, I or 2, of the envelope and a flange contacting the outer surface of that part adjacent the edge. At either or both places the contacting surfaces may be welded together. The parts I and 2 may be of any convenient metal, preferably steel, and the rings 3 and 4 are of an alloy which can be wetted by molten or softened glass, and which will have substantially the same coefficient of expansion as the glass.- It is also desirable that (Cl. Z-27.5)

the alloy selected be unaffected by the vapor in the tube.' especially when hot.

Between the rings 3 and 4 a glass iiange 5 integral with a sleeve 6 of the same material is interposed. The sleeve 6 forms a skirt within the tube depending from the seal and making a long leakage path separating the parts I and 2. The flange 5 is sealed to the rings 3 and 4. If preferred, the sleeve 6 and its ange 5 may be of refractory ceramic material and a body I0 of glass of the kind just described may be inserted in contact with the outer end of the flange 5. Outside of it, but with its inner part between the rings 3 and 4, a body II of refractory ceramic material may be placed in contact with the rings 3 and 4 and with the glass I0. The outer part of the body II is extended over the outside surfaces of flanges upon the rings, thereby affording a long leakage path on the outside of the tube between portions I and 2 of the envelope.

An alternative structure may be chosen in which the part I0 is refractory ceramic material and the parts 5 and II are glass. With either structure, the sealing may be accomplished by placing the completed tube in an oven and heating it to the point at which the glass softens or partially fuses, causing the glass portion to wet not only the rings but also the adjacent ceramic refractory parts making the whole seal a gas-tight structure.

For this method of sealing, it is preferable that the central portion I0 be the glass portion. The ceramic parts 5 and Il then act as Stoppers conm fming the glass while it is liquid or soft and also maintain the spatial separation between rings 3 and 4 while the glass is safe.

It is also possible to omit the parts Il] and II, in which case the part 5 must be of glass.

A seal may be made at the center of the part I and 'through it a conductor I5 extends to the grid I6. The seal for the lead I5 is in the center of a ring I1 of metal which will form a good seal with the glass. 'Ihis ring is welded to the adjacent portions of the part I. It comprises a sleeve extending into the interior of the tube and a flange overlapping the outside of the part l.

The seal comprises a portion I8 of glass forming a sealing contact both with the conductor i5 and with the inwardly extending sleeve of the ring I1. Inside of the tube the portion i8 is expanded, forming a skirt I9 which extends nearly into proximity with the grid I6. The skirt makes a long creepage path between the part I and the conductor I5.

The glass extends beyond the outer surface of the ring I1 but not very far because it must not' be exposed to the danger of being hit and broken. The distance vto which the glass extends above the ring depends on the necessary leakage path to properly insulate the grid I6 from the anode I.

The metal sleeve, extending well along the glass inside the tube, adds to the rigidity of the structure and can extend so far because the skirt I9 affords sufficient insulation in the comparatively short distance.

The grid I6 is spaced slightly from the end of the skirt, whereby the inner and outer surfaces of the skirt are both included in the leakage path. The opening between skirt and grid is narrow and at right angles to the boiling movement of mercury droplets. Mercury is, therefore, unlikely to enter the inside of the skirt and form a conductive coating on the inner glass surface.

The conductor I5 is hollow and its lower end is flanged to afford a good connection to the grid I6. This connection is preferably welded. The conductor |5 thus forms a duct through which the tube may be exhausted. After the tube is pumped, the duct may be closed by welding or if the tube is to be continually pumped during operation the duct may be kept open to the pump.

The cathode of this tube comprises a directly heated portion 20 which is connected by a lead 2| to the exterior of the tube. The portion 20 may be, as shown, a ribbon thick enough to support itself even when hot or it may be supported by a central refractory body as further described in connection with Fig. 2. In either case, it is coated with emissive material. The lead 2| passes through a body 22 of glass which can seal to the metal sleeve 23 extending from the bottom 24 of the tube. The bottom 24 is welded to the part 2 and its sleeve 23 may be made of the alloy described and welded to it. If desired, the bottom 24 may be made of steel and the sleeve 23 alone of the alloy.

The upper end of the directly heated portion 20 is welded to a cap 25 which, in its turn, is welded to a guard 26 and this, in its turn, is welded to inwardly extending projections on a shield 21, which surrounds the guard and the directly heated portion. A surface of the guard is coated with emissive material.

Surrounding the shield 21 is a second shield 28 which is welded to the shield 21 by inwardly off-set. portions at the top. At the bottom similar off-set portions of the shield 23 contact shield 21 but are not welded thereto. The bottom of the shield 28 has outwardly extending tabs or feet 29 by which it is secured, preferably by welding, to the plate 24. The plate 24 and the part 2 are welded together, a ange being provided on the bottom of the part 2 for securing an increased welding surface, as shown at 30.

The bottom of thc space enclosed by the guard 26 is closed by a disc 3| of refractory ceramic material which has a flange 32 extending into contact with the interior of the shield 21. The disc 3| has a radial slot 33 which accommodates a tap 34 extending from the lower end of the part 20 through the disc 3| where it is welded to the conductor 2|. This cathode structure as a whole, is supported from the plate 24.

The function of the structure is to delay the beginning of current from the anode to the cathode until the guard has had time to become sufficiently heated to emit electrons from its coated surface, as explained in greater detail ln my application Serial No. 57,536, filed January 4, 1936.

'I'he tubular conductor I5 and the lead 2| are coaxial with each other and with the envelope. Consequently'no attention need be paid when inserting the device into its connection, to the rotational position of this axis.

In the form of my device shown in Fig. 2, the part 20, the guard 26, the shield 21 and the shield 28 function as the corresponding parts of Fig. 1. The tab 34 is, however, at the upper end of the part 20 and the disc 3| of refractory ceramic material is at the top of the cathode structure. The off-set portions and welds described in connection with Fig. 1 are similar in Fig. 2. There are, however, some differences; the off-set prtions at the top of shields 21 and 28 are not welded and no, or at most, very little heating current flows through the shields or guard. At the bottom of the cathode structure a metal plate 3l is provided to which each of the several cylinders of the cathode structure are welded. From the tab 34, a hollow conductor 39 extends through a bore in the center of a. refractory insulator 40 to the exterior of the tube. provided with staggered teeth 4| which support the individual whorls of the part 2U. The top of the insulator 40 is fitted into a recess in the disc 3| which prevents relative movement between it and the other members of the cathode structure. Its bottom rests upon the top of a flanged ceramic member 42.

The flange of member 42 extends from a sleeve which fits a tube 43 which extends from the center of the plate 38 to the exterior of the tube. Within the tube 43 there is also fitted a glass portion 44 and a second portion 45 of ceramic insulation. The tube 43 is made of alloy which can form a sealed Joint with the glass 44. The plate 38 may be made of the same alloy and it and the sleeve 43 may be homogeneous, or if desired, the plate may be made of any selected metal, such as nickel, and the tube 43 welded thereto.

The envelope of the tube shown in Fig. 2 comprises. an anode 4B, which is essentially the shape of a bell jar and has a flange at the bottom shown at 41, by which it is welded to the bottom 4l. This bottom 4B has a 'central sleeve 49, integral therewith, or welded thereto, which is of the alloy aforementioned, capable of forming a seal with the glass. Within the tube 49 is fitted a body 5| of ceramic refractory material having at its upper end, which extends beyond the tube 49 into the interior of the tube, a flange or skirt 52. The flange 52 at the top of the body 5| makes a long creepage path between the cathode, which is electrically united with the sleeve 43 and the anode, which is electrically united with the sleeve 49.

Contacting with the bottom of the body is a body 53 of glass, capable of forming a seal with the aforesaid alloy, which fits the interior of the tube 49, and contacting with the bottom of the body 53 is a thimble-like member 54 of ceramic material, the outer surface of which flts the tube 49. The top of the member 54 is formed into an inwardly extending flange fitted to the exterior of the sleeve 43.

'I'he several insulating bodies 42, 44 and 45 have an aligned central bore through which the metallic tube 39 extends and the bodies of insulation 5|, 53 and 54 have a bore to accommodate the tube 53. The two bores, the tubes 43 and 49 and all the insulating bodies are coaxial, the common axis being the center of the tube 39. The exterior terminals of the anode, the cathode and the cathode heating circuit are thus three coaxial cylindrical metallic tubes.

'I'he inner one 39 is welded shut when the the device with respect The insulator 44 is pumping of the device is finished and when so welded forms a peg 55 which can be the inner terminal coaxial .with the exterior surface I9 and the intermediate surface 43. Nothing depends on the position rotationally of the tube, but the correct contact may be made even though the tube is rotated, about its conductor 39 as an axis. to any extent whatever. This device is a rectifier and has no control electrode like the grid i6 in Fig. i.

The tube in Fig. 3 has an anode 5i which is separated from the cathode part 62 of the envelope by a seal 53. Rings of appropriate sealing metal Gli and 55 are welded to the envelope portions 8| and 62 at the edges where the envelope joins the seal. The seal 63 consists of an outer portion of refractory material and an inner portion 66 of glass. This portion forms a flange on the sleeve 61. This sleeve constitutes a skirt from the seal 53 adding to the length of the leakage path on the inside of the envelope between the anode portion 6i and the cathode portion 62. The outside of the seal is extended, overlapping the rings 6G and 65,- and thus increasing the exterior leakage path between the anode portion of the envelope and the cathode portion thereof.

In the middle of the anode portion 5i a thimn ble 58 is provided having a iiange which contacts with the exterior of the portion 5i and may be welded thereto. The inwardly extending portion of the cup-shaped part of the thimble 58 is screwthreaded on its outer side which is inside of the envelope, and thus forms a threaded stud projecting into the interior of the tube. A graphite member 10 is screwed upon this stud and it is expanded into a skirt 1i which is electrically integral with the anode portion 6i of the envelope and projects nearly to the cathode. The cathode is formed by a pool 12 of mercury, which rests upon the bottom of the tube and is, therefore, electrically continuous with the portion 62 of the envelope. At the middle of the bottom of the envelope a terminal 13 is provided integral with the envelope portion 62.

An igniter, having a tip 15 of silicon carbide or boron carbide, is supported in contact with the pool 'l2 of`mercury, occupies the central position in the tube. The tip 15 is supported by a screw 1G formed on the end of a conductor 11. The conductor is surrounded by a glass seal 18 similar to the seal i8 in Fig. l, and ending in a skirt 19 similar to the skirt i9 in said figure.v Because the igniter structure is straight from the top of the device to the mercury pool, it is shorter and the structure is more rigid than it would otherwise be and because it is central there is good protection against shorting. The skirts 19 and 61 add'to this protection. This position of the igniter vgives a structure permitting closer spacing of the electrodes and skirt. An exhaust 86 is connected, preferably by welding, by a flange 8i to the anode part 6i of the envelope which is perforated at 82 for cooperation with the exhaust. The pipe may be permanently connected to a pump, or when the tube has been sufficiently exhausted, may be sealed off.

If it be desired to exhaust the tube of Fig. 3 through a conductor as the tubes of Figs. 1 and 2 are exhausted the conductor 11 may be hollow and an opening may be made in the side thereof in the part within the skirt 19. When this is done the pipe 8U will be omitted and no hole 82 provided. When the pumping is iinished the tube 11 may be closed by welding or otherwise.

The skirt 18 acts to increase the leakage path from thimble 58 to conductor 11. The extension of the bottom of the thimble along the glass 18 adds to the stiiness of the structure. The recess in the thimble accommodates the external part of the glass and also protects it from accidental injury. The externally extended glass also adds to the leakage path between the anode and the igniter.

When the mercury in the pool 12 is heated, mercury vapor rises into the interior of the anode portion 8i of the envelope and is condensed lthere to a greater extent than it is condensed in the lower space because the part 62 of the envelope is a good thermal conductor in contact with the pool 12. The condensed mercury, descending, forms droplets on the adjacent surfaces of anode skirt 51. The other or outer surface of the skirt 61 does not receive mercury droplets and so ai.- fords good leakage protection between the two portions of the envelopes 6i and 62. The interior of the skirt 19 is well protected from droplets both by the skirt itself and because the skirt is located in a hot region. It thus affords an eiective prevention against leakage.

The terminal stud 13 and the conductor 11 are in line with each other and are central of the envelope. Consequently the device can be put into working relation with the external connections in any postiion around this axis. It is not necessary to rotate the device about this axis into any particular position.

In the operation of the grid glow tube shown in Fig. l, the element 2l! is a source of electrons which are confined to thevinterior of the guard 26 until the guard has acquired suiicient tem.- perature to cause the oxide coating thereon to emit electrons. The guard is heated by heat from the member 20 and this heat is supplied by current which enters the lead 2i and departs mainly through the outer shield 28. To some extent shield 21 may conduct the current in parallel with shield 25 but not much because the junction at the bottom is not welded. Thence the current in through the feet 29 to the bottom 24 of the tube, the exterior of which constitutes at 23, the cathode terminal. The anode is connected by any'suitableexterior device to the positive potential. When the guard 26 has reached the proper temperature, the guard and the structure in its interior become a source of electrons which pass to the anode. The grid i6 is controlled through the conductor I5 and when it has a. sufciently negative' potential, prevents the anode current from starting.

In the rectifier shown in Fig.Y 2, the cathode structure acts like that described in Fig. 1, becoming a source of electrons as soon as the guard 26 has acquired suiiicient temperature to emit electrons from its coated surface. Current from the anode 46 through the gas in the tube to the cathode structure is possible after this temperature is acquired, butin the opposite direction, such current is not possible. This tube. therefore, acts as a rectier of alternating current. The connection, both to the heating circuit and to the circuit in which the current is to be rectiiled are made by inserting the device in its socket, no special positioning being needed as would be with the usual plurality of connecting pins. The direct heating o the cathode member 20 in this tube is by current which enters at the exterior end of tube 39 and departs from the sleeve I3. The current to be rectied has the sleeve 49 for one terminal and the sleeve 43 for the other terminal.

In the controlled arc device in Fig. 3, the current controlling the igniter 15 is introduced at the terminal 'Il and departs through the mercury I2 and the cathode terminal 13. The current to be conducted by the mercury arc is between the terminal I3 and any desirable connection to the exterior of the anode 6|. This current is controlled by the igniter 'l5 in a way familiar to those skilled in the art. It may be actuated by a dozen volts while the igniter requires some fifty to one hundred and fifty volts.

Many modifications beside those specically illustrated and described will occur to those skilled in the art, and I do not desire to be limited by the specific illustration and description oi the modication shown.

I claim as my invention:

1. A discharge device comprising a cathode structure having a directly heated source of electrons, a lead lor the heating current, a plurality of radiation shields therearound and `an electrostatic guard surrounding said directly heated a seal separating said lead from said portion, another portion of the envelope being electrically continuous with the anode and another seal separating said portions.

2. A discharge tube comprising a metallic envelope having two portions, one of which is electrically continuous with a cathode structure having a heated source of electrons and associated metallic parts, a support for said structure extending approximately the diameter o1' the tube, the other said portion of the envelope being electrically continuous with the anode, a seal separating said portions and having a skirt extending into the interior of the tube, a lead for the heating circuit, a return for the heating circuit including said support, and a seal concentric with and adjacent said first-named seal between said lead and said return, whereby all external terminals of cathode and anode have the same relative position independent of the rotational position of the tube.

3. A discharge device comprising a metallic velope, said seal having a skirt extending into the interior of the tube and providing a long leakage path on the inside of the tube between anode and cathode, and an insulating extension on the outside of the seal affording a long leakage path between anode and cathode on the outside of the tube.

4. A discharge device comprising a metallic envelope having two portions, one cf which is electrically continuous with the anode, the other said portion being electrically continuous with the cathode, an insulating seal separating saidportions and constituting a portion of the envelope, said seal having a skirt extending into the interior of the tube and providing a long leakage path on the inside of the tube between anode and cathode, and an insulating extension on the outside oJ the seal aii'ording a long leakage path betwetsA anode and cathode on the outside of i cally continuous the tube, a control electrode in said tube and a lead to said control electrode extending to the exterior of th envelope and a4 seal distinct from the first-named seal through which the lead extends.

5. A discharge device comprising a metal envelope having two portions, one of which is electrically continuous with the cathode structure, said structure comprising a source of electrons, a cylindrical guard around the source, and at least one radiation shield around said guard, said guard being electrically connected to said source of electrons at one end only, said guard being also electrically connected to one said portion of the envelope, the other said portion of the envelope being electrically continuous with the anode, and a body of insulation separating said portions of the envelope, said body of insulation having glass and ceramic materials, at least one of which forms a seal with the metal of the envelope.

6. A discharge device comprising a metallic envelope having two portions, one of which is electrically continuous with the anode structure and the other with the cathode structure, a body of insulation between said portions, said body including a part of material forming a sealing junction with the metal envelope and a part projecting from the gap between said two portions into the space within the device to form a skirt materially adding to the length of the interior leakage path between the cathode and anode.

7. A discharge tube comprising a metallic envelope having two portions, one oi' which is electrically continuous with a cathode structure having a heated source of electrons and associated metallic parts, a support for said structure extendlng approximately the diameter of the tube the other said portion of the envelope being electrically continuous with the anode, a seal separatlng said portions and having a skirt projecting from the gap between said two portions into the interior of the tube, a lead i'or the heating circuit, a return for the heating circuit including said support, and a seal between said lead and said return.

8. A discharge tube comprising a metallic envelope having two portions, one of which is electrically continuous with a cathode structure having a heated source of electrons and associated metallic parts, a support for said structure extending approximately the diameter of the tube the other said portion of the envelope being electriwith the anode, a seal separating said portions and having a skirt projecting from the gap between said two portions into the interior of the tube, a lead for the heating circuit, a return for the heating circuit including said support, and a seal concentric with said firstnamed seal, between said lead and said return.

A discharge device comprising a metallic `envelope having two portions, one of which is electrically continuous with the anode structure and the other with the cathode structure, bodies of insulation between said portions, at least one body being of a glassy material, at least one body being of ceramic material, one of said bodies forming a sealing Junction with the metal envelope and one of said bodies having a part extending within the device to form a skirt materially adding to the length of the interior leakage path between the cathode and anode.

ERWIN F. LOWRY. 

